1. Field of the Invention
The present invention relates to improved methods and compositions for sealing subterranean zones penetrated by well bores.
2. Description of the Prior Art
In the drilling of oil and gas wells using the rotary drilling method, drilling fluid is circulated through the drill string and drill bit and then back to the surface by way of the well bore being drilled. The drilling fluid maintains hydrostatic pressure on the subterranean zones through which the well bore is drilled and circulates cuttings out of the well bore. During such drilling, subterranean vugs, fractures and other thief zones are often encountered whereby the drilling fluid circulation is lost and drilling operations must be terminated until remedial steps are taken. In addition to drilling fluid lost circulation zones, zones containing pressurized fluids can be encountered which cause undesirable gas, oil or water production into the well bore or cross-flows through the well bore.
Heretofore, sealing compositions comprised of sodium silicate solutions have been used to control lost circulation and terminate undesirable fluid production and cross-flows in subterranean zones. When such a sodium silicate sealing composition is placed in a subterranean zone, the sodium silicate solution is polymerized or cross-linked whereby a pliable gel is formed which functions to temporarily reduce or terminate lost circulation, undesirable fluid production or cross-flows. Thereafter, the zone has typically been cemented utilizing a conventional cement slurry.
While the heretofore utilized procedures described above have often been used successfully, they are relatively time consuming and expensive to carry out. Consequently, there is a continuing need for improved more economical subterranean zone sealing methods and compositions which can be utilized in subterranean zones to terminate lost circulation, undesirable fluid production, cross-flow zones or the like.